1. Definition:

2. Period:

Though lactation starts towards the end of pregnancy but a free flow of milk occurs only after the child birth. It can be continued after the birth only if the child continues to suckle.

3. Mechanism:

Lactation involves two phases:

(i) Milk secretion:

It involves the synthesis of milk by alveolar epithelium of the mammary glands and its passage through the duct system. It is regulated by increased secretion of prolactin hormone from the adenohypophysis of pituitary gland due to decrease in level of estrogens and progesterone after the child birth. This initiation of milk formation is called lacto-genesis.

Galactopoeisis is the maintenance of milk secretion. It is regulated by a number of hormonal factors like growth hormone, thyroxine and Cortisol. It occurs upto 7 to 9 months after the child birth. Suckling of nipple by baby initiates the impulses which stimulate the hypothalamus to secrete Prolactin Releasing Factor (PRF) which stimulates increased secretion of prolactin.

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(ii) Milk ejection:

It involves discharge of milk from the mammary glands. Suckling of nipple by the baby stimu­lates the touch receptors present around the nipple. The impulses initiated by touch receptors are carried to hypo­thalamus and neurohypophysis which secrete and re­lease the oxytocin hormone respectively.

Oxytocin causes the forceful contraction of myoepithelial cells present around the alveoli of the mammary glands. This causes the ejection of milk from the alveoli of the mammary glands.

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So the lactation is controlled by a neuroendocrine reflex, also called milk let-down reflex.

4. Composition of milk:

5. Significance:

Milk helps the mother in feeding the newly born. The milk produced during the initial few days of lactation is called colostrum. It is rich in proteins and calories. It also contains certain antibodies which provide passive immunity to the new born. So breast feeding during the initial period of infant growth is good for bringing up a healthy baby.